1. Field of the Invention
The invention relates to an engine brake for a multicylinder internal combustion engine, with valves that can be briefly opened periodically, in each case outside the exhaust stroke.
2. Description of the Related Art
Recently, not only exhaust brakes but so-called decompression brakes have gained a foothold for engine braking systems; they make the compression work of the compression stroke useful for braking by blowoff in the region of the ignition top dead center. This is done by slight or brief opening of the outlet valve or of an additional small valve; metering of the braking output can be done by controlling the opening times. Various models of these decompression brakes have been introduced, for instance in a special printing of ATZ Automobiltechnische Zeitschrift [Automobile Engineering Journal] 90 (1988), No. 12, in the article entitled "Die Motorbremse von Nutzfahrzeugen --Grenzen und Moglichkeiten zur Weiterentwicklung" [Engine Brakes in Utility Vehicles--Limits and Opportunities for further Development]. One model for instance provides that with the engine brake turned on, the outlet valves are also opened at the end of any given compression stroke, via telescopingly extendable valve tappets. The telescoping extension of the valve tappets is done via positive displacement pistons, which are driven by a cam located on the inside, while the return of the valve tappets to the normal length is done via unlockable check valves, which are opened and closed simultaneously by a central, pneumatically triggered control disk. However, the known control circuit has a relatively complex structure in terms of circuitry and equipment, which also makes its assembly complicated and expensive. Controlling the valves exactly in terms of time also presents difficulties, especially at high rpm.
German Patent 30 26 529 discloses a decompression engine brake for a multicylinder internal combustion engine, in which a controllable telescoping part embodied as a piston, which is disposed in the valve tappet and is hydraulically actuated, is provided in the valve linkage of the applicable outlet valves, in order to vary the effective length of this linkage in the direction of an opening movement of the outlet valve. Triggering the telescoping part is done via individual control lines, to each of which one positive displacement piston is assigned. The positive displacement pistons are guided radially in a housing and are driven by an inner cam, which is rotated synchronously with the camshaft. For each individual pump piston, one unlockable check valve is provided; a central, pneumatically triggered control disk serves to open and close all the check valves simultaneously.
Because in this known case a separate pump with a control circuit is assigned to each individual cam drive, the structure in terms of circuitry and apparatus is relatively complex. This not only makes assembly of the components required for the engine brake difficult, but with this known apparatus it also becomes difficult to control the valves correctly in terms of time, especially at high rpm, and thus to meter the engine brake correctly.
European Patent Disclosure A 83058 discloses an engine brake in which a central pump is used. However, for each engine valve to be actuated, one dispenser piston and one receiver piston are provided; the receiver piston actuates the engine valve, and the dispenser piston is actuated indirectly by the camshaft. A hydraulic valve is connected to the output side of the pump, but it has solely an activation and filling function for the engine brake system. Accordingly, this hydraulic valve simply performs the function of turning the engine brake on and off. Because of the provision of a separate dispenser and receiver piston for each engine valve, the structure of the engine brake continues to be relatively complex.